1. Field of the Invention
The present invention relates to a phototransistor and a semiconductor device.
2. Description of the Related Art
A phototransistor of which the sensor can amplify a photoelectric current generated by p-n junction because of its bipolar structure, and is used as a highly-sensitive photodetector. For example, the phototransistor is used in a sensor that measures the smoothness of a recording medium such as a sheet of paper. Specifically, the recording medium is irradiated with light by a light source such as an LED, and the phototransistor receives a weak reflected light from the recording medium thereby outputting a photoelectric current, and the smoothness is measured on the basis of the photoelectric current.
Furthermore, conventionally, there has been disclosed a technology to form an extremely-small emitter region, thereby improving the frequency response of a bipolar transistor or a phototransistor.
However, a conventional phototransistor may fail to accurately output a photoelectric current if only a part of a light-receiving region of the phototransistor is irradiated with light.
Therefore, there is a need to provide a phototransistor and semiconductor device capable of outputting a photoelectric current with high accuracy.